Climate-friendly metals from deep-sea ores
The Düsseldorf-based Max Planck team is extracting elemental copper from deep-sea ores simply by melting them in an electric arc furnace. Reduction using hydrogen plasma then produces an alloy containing, amongst other elements, nickel and cobalt. This process emits 90 per cent less CO₂ and requires almost a fifth less energy than the conventional method, which is based on reduction using coal. Metals required for the energy transition could thus be produced with low CO₂ emissions.
The climate-friendly transformation of the economy is only possible through the electrification of industrial processes, transport and heat generation. For example, around 60 million tonnes of copper will be needed by 2050 for electric motors and the expansion of the electricity grid, and, depending on future developments in battery technology, 10 million tonnes of nickel and 1.4 million tonnes of cobalt will also be required. Demand for copper and nickel would therefore more than double by the middle of the century, whilst demand for cobalt would increase approximately fivefold. The mining of metals always takes a toll on the environment. For instance, large areas of forest are repeatedly cleared to make way for nickel and cobalt mines. And cobalt mining in particular usually takes place under highly questionable social conditions: according to the UN Children’s Fund, children are often even sent into the mines for this purpose. Furthermore, the ores found on land now contain only a very small proportion of the metals sought. For every tonne of copper extracted from onshore deposits, 200 tonnes of waste are produced, and overall, the production of copper, nickel and cobalt generates a total of four to five billion tonnes of unusable rock and slag annually.
An alternative to onshore mining is the extraction of deep-sea ore nodules, often referred to as manganese nodules, which contain not only large quantities of manganese but also a considerable proportion of copper, nickel and cobalt. They are found in large quantities in the Clarion-Clipperton Zone in the Pacific Ocean. A team from the Max Planck Institute for Sustainable Materials (MPI-SusMat) has now presented an efficient, low-carbon process in the journal *Science Advances* in which copper, nickel and cobalt can be extracted from deep-sea ores through smelting and reduction with hydrogen. The method is significantly more sustainable than the process used by the Canadian company TMC in its Nori-D project, which involves reducing deep-sea ores using coal. This is because hydrogen reduction not only produces 90 per cent less CO₂ when carried out using green hydrogen and electricity. The Max Planck team’s approach also requires almost 20 per cent less energy and fewer process steps.
No deforestation and significantly less waste from deep-sea mining
“The extraction of these metal nodules in the deep sea also leaves an ecological footprint,” says Dierk Raabe, Director at MPI-SusMat. “That is why, just a few years ago, I was opposed to exploiting these resources, so as not to repeat the same mistakes we have made on land.” However, the materials scientist is now open to deep-sea mining, at least provided it is carried out in the most environmentally sustainable way possible. One of the reasons he has changed his mind is that the extraction of metals from deep-sea ores does not involve child labour, does not lead to large-scale deforestation and produces significantly less waste. For instance, producing the metals for one billion electric car batteries would generate nine billion tonnes of rock waste if the materials were extracted from deep-sea ores, whereas extracting them from onshore deposits would require 63 billion tonnes of unusable rock to be sent to landfill. This has been calculated by researchers at the University of Delaware.
The environmental footprint of metal production from deep-sea ores would also be reduced by the process developed by the Max Planck researchers. “We reduce the dried ores using a hydrogen plasma directly in an electrically powered arc furnace,” explains Ubaid Manzoor, who carried out the experiments as part of his PhD. The researchers are already able to recover almost all of the copper as pure metal by melting the ore and then allowing the melt to cool slightly. As soon as they then allow hydrogen to flow into the furnace, various manganese oxides – some of which can be used in batteries – are produced, along with an alloy comprising, amongst other things, copper, nickel and cobalt. The proportions in the alloy vary depending on the duration of the reduction. “Because we can separate out the copper beforehand, it becomes easier to process the remaining alloy further,” says Ubaid Manzoor. In an earlier study, the research team led by Ubaid Manzoor had already presented a very similar process for extracting nickel in a climate-friendly way from ores mined on land.
A contribution to the comprehensive life cycle assessment of deep-sea mining
The extent to which deep-sea ore mining will one day replace onshore mining is still the subject of international negotiations. “However, through our work, we aim to provide information that can be used to comprehensively assess the environmental impacts of metal production from various deposits,” says Ubaid Manzoor. And for Dierk Raabe, one thing is clear: “If we want to move away from a carbon-intensive economy, we’ll have to bite the bullet.”
Source: MPI-SusMat